P-type doping layers for use with light emitting devices

ABSTRACT

A light emitting diode (LED) comprises an n-type Group III-V semiconductor layer, an active layer adjacent to the n-type Group III-V semiconductor layer, and a p-type Group III-V semiconductor layer adjacent to the active layer. The active layer includes one or more V-pits. A portion of the p-type Group III-V semiconductor layer is in the V-pits. A p-type dopant injection layer provided during the formation of the p-type Group III-V layer aids in providing a predetermined concentration, distribution and/or uniformity of the p-type dopant in the V-pits.

RELATED APPLICATIONS

This application is a Continuation Application of pending U.S.Non-Provisional application Ser. No. 14/133,162 filed on Dec. 18, 2013,now U.S. Pat. No. 8,828,752 issued on Sep. 9, 2014, which is aDivisional Application of pending U.S. Non-Provisional application Ser.No. 13/248,821 filed on Sep. 29, 2011, now U.S. Pat. No. 8,698,163issued on Apr. 15, 2014, the contents of which are all hereinincorporated by reference in their entireties.

BACKGROUND

Lighting applications typically use incandescent or gas-filled bulbs.Such bulbs typically do not have long operating lifetimes and thusrequire frequent replacement. Gas-filled tubes, such as fluorescent orneon tubes, may have longer lifetimes, but operate using high voltagesand are relatively expensive. Further, both bulbs and gas-filled tubesconsume substantial amounts of energy.

A light emitting diode (LED) is a device that emits light upon therecombination of electrons and holes in an active layer of the LED. AnLED typically includes a chip of semiconducting material doped withimpurities to create a p-n junction. Current flows from the p-side, oranode, to the n-side, or cathode. Charge-carriers—electrons andholes—flow into the p-n junction from electrodes with differentvoltages. When an electron meets a hole, the electron recombines withthe hole in a process that may result in the radiative emission ofenergy in the form of one or more photons (hv). The photons, or light,are transmitted out of the LED and employed for use in variousapplications, such as, for example, lighting applications andelectronics applications.

LED's, in contrast to incandescent or gas-filled bulbs, are relativelyinexpensive, operate at low voltages, and have long operating lifetimes.Additionally, LED's consume relatively little power and are compact.These attributes make LED's particularly desirable and well suited formany applications.

Despite the advantages of LED's, there are limitations associated withsuch devices. Such limitations include materials limitations, which maylimit the efficiency of LED's; structural limitations, which may limittransmission of light generated by an LED out of the device; andmanufacturing limitations, which may lead to high processing costs.Accordingly, there is a need for improved LED's and methods formanufacturing LED's.

SUMMARY

An aspect of the invention provides light emitting devices, such aslight emitting diodes (LED's). In an embodiment, a light emitting diodeincludes an n-type gallium nitride (GaN) layer, which is doped with ann-type dopant, and an active layer adjacent to the n-type GaN layer. Theactive layer can have one or more V-pits. A p-type GaN layer is adjacentto the active layer. The p-type GaN layer is doped with a p-type dopant.The p-type GaN layer includes a first portion and a second portionlaterally bounded by the one or more V-pits. The first portion isdisposed over the active layer. The second portion has a uniformconcentration of a p-type dopant.

In another embodiment, a light emitting diode (LED) includes a siliconsubstrate and an n-GaN layer adjacent to the silicon substrate. Anactive layer is adjacent to the n-GaN layer and an electron blockinglayer is adjacent to the active layer. A p-GaN layer is adjacent to theelectron blocking layer. The LED comprises Mg and In at an interfacebetween the electron blocking layer and the p-GaN layer.

In another embodiment, a light emitting device includes a first layer,which has n-type gallium nitride (GaN), and a second layer adjacent tothe first layer. The second layer includes an active material configuredto generate light upon the recombination of electrons and holes. Thesecond layer further includes one or more V-pits. A third layer isadjacent to the second layer. The third layer includes p-type GaN havinga uniform distribution of a p-type dopant across a portion of the thirdlayer extending into the one or more V-pits.

In another embodiment, a light emitting diode (LED) includes a firstlayer, which has n-type gallium nitride (GaN), and a second layeradjacent to the first layer. The second layer includes an activematerial configured to generate light upon the recombination ofelectrons and holes. A third layer is disposed adjacent to the secondlayer. The third layer includes a p-type dopant and a wetting materialconfigured to enable the p-type dopant to uniformly distribute in thethird layer.

In another embodiment, a light emitting diode includes an n-type galliumnitride (GaN) layer and an active layer adjacent to the n-type GaNlayer. The active layer can have one or more V-pits. A p-type GaN layeris adjacent to the active layer. The p-type GaN layer includes a firstportion and a second portion laterally bounded by the one or moreV-pits. The first portion is disposed over the active layer. The secondportion has a concentration of a p-type dopant of at least about ×10¹⁹cm⁻³.

In another embodiment, a light emitting diode includes a first layer,which has either an n-type gallium nitride (GaN) or a p-type GaN, and anactive layer. The active layer is adjacent to the first layer and canhave one or more V-pits. The light emitting diode further includes asecond layer having either the n-type GaN or p-type GaN that was notused in the first layer. In other words the first and second layer eachhave a different one of the n-type GaN or p-type GaN materials. Thesecond layer includes a first portion and a second portion. The secondportion is laterally bounded by the one or more V-pits. The firstportion is disposed over the active layer. The second portion has auniform concentration of a p-type dopant.

In another embodiment, a light emitting device includes a first layer,which has either an n-type Group III-V semiconductor or a p-type GroupIII-V semiconductor, and an active layer. The active layer is adjacentto the first layer and can have one or more V-pits. The light emittingdiode further includes a second layer having either the n-type GroupIII-V semiconductor or the p-type Group III-V semiconductor that was notused in the first layer. In other words the first and second layer eachhave a different one of the n-type Group III-V semiconductor or thep-type Group III-V semiconductor. The second layer includes a firstportion and a second portion. The second portion is laterally bounded bythe one or more V-pits, and the first portion is disposed over theactive layer. The second portion has a uniform concentration of a p-typedopant.

Another aspect of the invention provides methods for forming lightemitting devices, such as light emitting diodes. In an embodiment, amethod for forming a light emitting diode includes delta doping awetting layer with a p-type dopant. The wetting layer is formed adjacentto an electron blocking layer, and the electron blocking layer is formedadjacent to an active layer. The active layer is formed adjacent to ann-type Group III-V semiconductor layer, and the n-type Group III-Vsemiconductor layer is formed adjacent to a substrate. In someembodiments, the wetting layer is in direct contact with the electronblocking layer. In some embodiments, the electron blocking layer is indirect contact with the active layer. In some embodiments, the activelayer is in direct contact with the n-type Group III-V semiconductorlayer.

In another embodiment, a method for forming a light emitting device,such as a light emitting diode, includes forming, over a substrate in areaction chamber (or reaction space if the reaction chamber includes aplurality of reaction spaces), a p-type Group III-V semiconductor layeradjacent to an active layer. The p-type Group III-V semiconductor layerextends into one or more V-pits of the active layer. The p-type GroupIII-V semiconductor layer is formed by delta doping a wetting layer witha p-type dopant, and introducing a source gas of a Group III species anda source gas of a Group V species into the reaction chamber. In somesituations, the wetting layer is formed adjacent to the active layer. Inan example, the wetting layer is formed on the active layer.

Additional aspects and advantages of the present disclosure will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein only illustrative embodiments of thepresent disclosure are shown and described. As will be realized, thepresent disclosure is capable of other and different embodiments, andits several details are capable of modifications in various obviousrespects, all without departing from the disclosure. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the features and advantages of the presentinvention will be obtained by reference to the following detaileddescription that sets forth illustrative embodiments, in which theprinciples of the invention are utilized, and the accompanying drawingsof which:

FIG. 1 schematically illustrates a light emitting diode;

FIG. 2 schematically illustrates a light emitting diode with a region ofinadequately doped p-type gallium nitride (p-GaN) filling V-defects ofthe active layer;

FIG. 3 schematically illustrates a light emitting diode having a p-GaNlayer adjacent to an active layer;

FIG. 4 schematically illustrates a light emitting device with a deltadoped layer, in accordance with an embodiment;

FIG. 5 schematically illustrates a light emitting device with a deltadoped layer and other device layers, in accordance with an embodiment;

FIG. 6 shows a method for forming a light emitting device, in accordancewith an embodiment; and

FIG. 7 shows pressure vs. time pulsing plots used to form a Mg deltadoped layer and a p-GaN layer.

DETAILED DESCRIPTION

While various embodiments of the invention have been shown and describedherein, it will be obvious to those skilled in the art that suchembodiments are provided by way of example only. Numerous variations,changes, and substitutions may occur to those skilled in the art withoutdeparting from the invention. It should be understood that variousalternatives to the embodiments of the invention described herein may beemployed in practicing the invention.

The term “light emitting device,” as used herein, refers to a deviceconfigured to generate light upon the recombination of electrons andholes in a light emitting region (or “active layer”) of the device. Alight emitting device in some cases is a solid state device thatconverts electrical energy to light. A light emitting diode (“LED”) is alight emitting device. There are examples of LED device structures thatare made of different materials and have different structures andperform in a variety of ways. Some LED's emit laser light, and othersgenerate non-monochromatic light. Some LED's are optimized forperformance in particular applications. An LED may be a so-called blueLED comprising a multiple quantum well (MQW) active layer having indiumgallium nitride. A blue LED may emit non-monochromatic light having awavelength in a range from about 440 nanometers to 500 nanometers whilehaving an average current density of 38 amperes per square centimeter ormore. A phosphor coating may be provided that absorbs some of theemitted blue light. The phosphor in turn fluoresces to emit light ofother wavelengths so that the light the overall LED device emits has awider range of wavelengths.

The term “layer,” as used herein, refers to a layer of atoms ormolecules on a substrate. In some cases, a layer includes an epitaxiallayer or a plurality of epitaxial layers. A layer may include a film orthin film, or a plurality of films or thin films. In some situations, alayer is a structural component of a device (e.g., light emitting diode)serving a predetermined device function, such as, for example, an activelayer that is configured to generate light. A layer generally has athickness from about one monoatomic monolayer (ML) to tens ofmonolayers, hundreds of monolayers, thousands of monolayers, millions ofmonolayers, billions of monolayers, trillions of monolayers, or more. Inan example, a layer is a multilayer structure having a thickness greaterthan one monoatomic monolayer. In addition, a layer may include multiplematerial layers. In an example, a multiple quantum well active layerincludes multiple well and barrier layers.

The term “active region” (or “active layer”), as used herein, refers toa light emitting region of a light emitting diode (LED) that isconfigured to generate light. An active layer includes an activematerial that generates light upon the recombination of electrons andholes. An active layer may include one or a plurality of layers. In somecases, an active layer includes a barrier layer (or cladding layer, suchas, e.g., GaN) and a quantum well (“well”) layer (such as, e.g., InGaN).In an example, an active layer comprises multiple quantum wells, inwhich case the active layer may be referred to as a multiple quantumwell (“MQW”) active layer.

The term “doped,” as used herein, refers to a structure or layer that isdoped with a doping agent. A layer may be doped with an n-type dopant(also “n-doped” herein) or a p-type dopant (also “p-doped” herein). Insome cases, a layer is undoped or unintentionally doped (also “u-doped”or “u-type” herein). In an example, a u-GaN (or u-type GaN) layerincludes undoped or unintentionally doped GaN.

The term “dopant,” as used herein, refers to a doping agent, such as ann-type dopant or a p-type dopant. P-type dopants include, withoutlimitation, magnesium, zinc and carbon. N-type dopants include, withoutlimitation, silicon and germanium. A p-type semiconductor is asemiconductor that is doped with a p-type dopant. An n-typesemiconductor is a semiconductor that is doped with an n-type dopant. Ann-type Group III-V semiconductor includes a Group III-V semiconductorthat is doped n-type, such as n-type gallium nitride (“n-GaN”). A p-typeGroup III-V semiconductor includes a Group III-V semiconductor that isdoped p-type, such as p-type GaN (“p-GaN”).

The term “adjacent” or “adjacent to,” as used herein, includes ‘nextto’, ‘adjoining’, ‘in contact with’, and ‘in proximity to’. In someinstances, adjacent components are separated from one another by one ormore intervening layers. For example, the one or more intervening layerscan have a thickness less than about 10 micrometers (“microns”), 1micron, 500 nanometers (“nm”), 100 nm, 50 nm, 10 nm, 1 nm, or less. Inan example, a first layer is adjacent to a second layer when the firstlayer is in direct contact with the second layer. In another example, afirst layer is adjacent to a second layer when the first layer isseparated from the second layer by a third layer.

The term “substrate,” as used herein, refers to any workpiece on whichfilm or thin film formation is desired. A substrate includes, withoutlimitation, silicon, silica, sapphire, zinc oxide, carbon (e.g.,graphene), SiC, AN, GaN, spinel, coated silicon, silicon on oxide,silicon carbide on oxide, glass, gallium nitride, indium nitride,titanium dioxide, aluminum nitride, a metallic material (e.g.,molybdenum, tungsten, copper, aluminum), and combinations (or alloys)thereof.

The term “injection efficiency,” as used herein, refers to theproportion of electrons and holes passing through a light emittingdevice that are injected into the active region of the light emittingdevice.

The term “internal quantum efficiency,” as used herein, refers to theproportion of all electron-hole recombination events in an active regionof a light emitting device that are radiative (i.e., producing photons).

The term “extraction efficiency,” as used herein, refers to theproportion of photons generated in an active region of a light emittingdevice that escape from the device.

The term “external quantum efficiency” (EQE), as used herein, refers tothe ratio of the number of photons emitted from an LED to the number ofelectrons passing through the LED. That is, EQE=Injectionefficiency×Internal quantum efficiency×Extraction efficiency.

LED's may be formed of various semiconductor device layers. In somesituations, Group III-V semiconductor LED's offer device parameters(e.g., wavelength of light, external quantum efficiency) that may bepreferable over other semiconductor materials. Gallium nitride (GaN) isa binary Group III-V direct bandgap semiconductor that may be used inoptoelectronic applications and high-power and high-frequency devices.

Group III-V semiconductor based LED's may be formed on varioussubstrates, such as silicon or sapphire. Silicon provides variousadvantages over other substrates, such as the capability of usingcurrent manufacturing and processing techniques, in addition to usinglarge wafer sizes that aid in maximizing the number of LED's formedwithin a particular period of time. FIG. 1 shows an LED 100 having asubstrate 105, an AlGaN layer 110 adjacent to the substrate 105, a pitgeneration layer 115 adjacent to the AlGaN layer 110, an n-type GaN(“n-GaN”) layer 120 adjacent to the pit generation layer 115, an activelayer 125 adjacent to the n-GaN layer 120, an electron blocking (e.g.,AlGaN) layer 130 adjacent to the active layer 125, and a p-type GaN(“p-GaN”) layer 135 adjacent to the electron blocking layer 130. Theelectron blocking layer 130 is configured to minimize the recombinationof electrons with holes in the p-GaN layer 135. The substrate 100 may beformed of silicon. In some cases, the pit generation layer 115 comprisesunintentionally doped GaN (“u-GaN”).

While silicon provides various advantages, such as the ability to usecommercially available semiconductor fabrication techniques adapted foruse with silicon, the formation of a Group III-V semiconductor-based LEDon a silicon substrate poses various limitations. As an example, thelattice mismatch and coefficient of thermal expansion between siliconand gallium nitride leads to structural stresses that generate defectsupon the formation of gallium nitride thin films, such as threadingand/or hairpin dislocations (collectively “dislocations” herein). Thinfilm growth around the defects produces V-defects (or V-pits), which areV-shaped or generally concave structures in device layers. Such V-pitsmake it difficult to achieve uniform device properties, such as thedistribution of dopants in one or more layers.

For instance, p-type doping of GaN grown within V-defect pits(collectively, “V-pits” herein) after the formation of an aluminumgallium nitride (Al GaN) layer may be insufficient to enable efficienthole emission from the material filling the V-defect in the activeregion. This problem may be due to the tendency of the p-type dopant(e.g., Mg) to segregate to the c-plane of an Al GaN surface as opposedto faceted V-defect AlGaN surfaces during thin film formation. Theadsorption of the p-type dopant at V-defect faceted surfaces may berelatively insensitive to the gas phase p-type dopant precursorconcentration. The incorporation of the p-type dopant takes placeprimarily along the c-plane surface. FIG. 2 shows an example of theresulting LED. The GaN material filling the pit is inadequately doped,resulting in poor device performance (e.g., low brightness, high powerinput) and/or non-uniform light output across the LED. That is, in casesin which the doping distribution of p-type dopant is non-uniform in thep-type GaN (p-GaN) layer, the electronic structure (or band diagram) ofthe LED may vary across the device, leading to a distribution of emittedlight that is non-uniform. In the illustrated example, a portion of thep-type layer in the V-defects is undoped and therefore lacking aconcentration of a p-type dopant (e.g., Mg) required for desirable(e.g., uniform) device performance. The portion of the p-type layer inthe V-pits is inadequately doped, having a p-type dopant concentrationthat is less than the concentration of the p-type dopant in the p-GaNlayer outside of the V-pits. In an example, the p-GaN layer in theV-pits has a p-type dopant concentration that is at most 1%, or 10%, or20%, or 30%, or 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 95% thatof the concentration of the p-type dopant in the p-GaN layer outside ofthe V-pits.

An approach for addressing such issues includes growing p-GaN with a lowconcentration of indium directly on the V-defect pitted active regionbefore the AlGaN, thereby reducing the problem of p-type dopant (e.g.,Mg) segregation on an AlGaN surface. A light emitting device having sucha structure is shown schematically in FIG. 3. Although hole injectionefficiency is achieved, at least some of the benefit derived by havingan intervening electron blocking layer between the active layer and thep-GaN may be lost.

Another approach for addressing such issues is to minimize theconcentration of V-pits in the LED. For example, the active layer may beformed with low or substantially low defect densities, which may aid inminimizing the coverage (or density) of V-pits. Such an approach,however, may be commercially infeasible and/or difficult to implementwith methods currently available for forming LED's. For instance, theformation of LED component layers (e.g., active layer) at low defectdensities may be a slow and resource intensive process, leading to highprocessing costs and inadequate device turnover to meet the commercialdemand for LED devices.

Provided herein are device structures and methods for reducing, if noteliminating, the issues with inadequate dopant concentrations in V-pits.Devices and methods provided herein advantageously preclude the need forforming LED component layers with low defect densities by compensatingfor the issues of poor and/or non-uniform dopant concentrations invarious LED component layers.

Light emitting devices and methods described in various embodiments ofthe invention address the problem of inefficient p-type doping in V-pitsdue to p-type dopant segregation to the c-plane of an AlGaN surfaceduring the formation of the p-GaN layer. Methods and structuresdescribed herein provide for high hole injection efficiency without ap-type semiconductor layer below the Al GaN electron blocking layer (seeFIG. 3).

Light Emitting Devices

In an aspect of the invention, light emitting device structures areprovided having improved dopant concentrations in V-pits. Such devicestructures minimize or preclude the need to form light emitting devicestructures with minimal defect densities. With the aid of structuresprovided herein, device structures with relatively moderate defectdensities (and hence V-pits) may be used, which advantageously reducesprocessing costs.

In some embodiments, a light emitting device, such as a light emittingdiode (LED), comprises a first layer of one of an n-type Group III-Vsemiconductor and a p-type Group III-V semiconductor, an active layeradjacent to the first layer, and a second layer of the other of then-type Group III-V semiconductor and the p-type Group III-Vsemiconductor adjacent to the active layer. The n-type Group III-Vsemiconductor comprises a Group III-V semiconductor that is doped withan n-type dopant. The p-type Group III-V semiconductor comprises a GroupIII-V semiconductor that is doped with a p-type dopant. The active layerincludes one or more V-pits. The second layer has a first portion and asecond portion laterally bounded by the one or more V-pits. The firstportion is disposed over the active layer. The second portion has auniform concentration of an n-type or p-type dopant. In an example, theGroup III-V semiconductor is gallium nitride. In some embodiments, theactive layer has a defect density between about 1×10⁸ cm⁻² and 5×10⁹ cm⁻². In other embodiments, the active layer has a defect density betweenabout 1×10⁹ cm⁻² and 2×10⁹ cm⁻².

The Group III-V semiconductor includes a Group III species and a Group Vspecies. In some embodiments, the Group III species is gallium and theGroup V species is nitrogen. In some embodiments, the Group III speciesincludes gallium and/or indium. In other embodiments, the Group IIIspecies includes gallium, indium and/or aluminum.

In some embodiments, a light emitting device includes an n-type galliumnitride (GaN) layer having an n-type dopant. The n-GaN layer is disposedadjacent to an active layer that has one or more V-pits. That is, theactive layer, as formed, exhibits one or more V-shaped pits (ordefects). The active layer is adjacent to a p-type GaN layer having ap-type dopant. The p-GaN layer has a first portion and a second portion.The second portion is laterally bounded by the one or more V-pits. Thefirst portion is disposed over the active layer and not laterallybounded by the one or more V-pits. In an embodiment, the light emittingdevice is a nascent light emitting device, requiring additionalprocessing and/or device structures to reach completion.

In some cases, the p-GaN layer has a thickness ranging between about 10nanometers (“nm”) and 1000 nm. In other embodiments, the p-GaN layer hasa thickness ranging between about 50 nm and 500 nm. The thickness of thep-GaN layer may be selected so as to provide a light emitting devicehaving predetermined operating conditions.

In some cases, the n-GaN layer has a thickness ranging between about 100nm and 8 micrometers (“microns”), whereas in other embodiments thethickness of the n-GaN layer ranges between about 500 nm and 6 microns.In yet other embodiments, the thickness of the n-GaN layer rangesbetween about 1 micron and 4 microns. The thickness of the n-GaN layermay be selected so as to provide a light emitting device havingpredetermined operating conditions.

In an embodiment, the p-type dopant includes one or more of magnesium,carbon and zinc. In a particular implementation, the p-type dopant ismagnesium.

In an embodiment, the n-type dopant includes one or more of silicon andgermanium. In a particular implementation, the n-type dopant is silicon.

In some situations, the p-GaN layer further comprises a wetting materialthat aids in the doping of the p-GaN layer. The wetting material in somecases enables the p-type dopant to uniformly distribute across a layerof the wetting material prior to the formation of the p-GaN layer (seebelow). In some situations, the wetting material is indium (In).

In some embodiments, the second portion has a uniform concentration ofthe p-type dopant. In some cases, the concentration of the p-type dopantin the second portion is nearly or substantially equal to theconcentration of the p-type dopant (or another p-type dopant) in thefirst portion of the p-GaN layer. In an embodiment, the concentration ofthe p-type dopant in the second portion is within about 90%, or 80%, or70%, or 60%, or 50%, or 40%, or 30%, or 20%, or 10%, or 5%, or 1%, or0.1%, or 0.01%, or 0.001% of the concentration of the p-type dopant inthe first portion.

In an embodiment, the second portion is substantially doped with ap-type dopant. The concentration of the p-type dopant in the firstportion and the second portion is between about 1×10^(18 cm) ⁻³ and1×10²² cm⁻³. In other embodiments, the concentration of the p-typedopant in the first portion and the second portion is between about1×10¹⁹ cm⁻³ and 1×10²¹ cm⁻³, while in other embodiments, theconcentration of the p-type dopant in the first portion and the secondportion is between about 1×10²⁰ cm⁻³ and 5×10²⁰ cm⁻³.

In other situations, the concentration of the p-type dopant in the firstportion is at a maximum at or near the active layer and decreases towardthe second portion. In other situations, the concentration of the p-typedopant in the first portion is uniform or substantially uniform along adirection parallel to a surface between the p-GaN layer and the activelayer (also “lateral axis” herein) and along a direction orthogonal to asurface between the p-GaN layer and the active layer (also “longitudinalaxis” herein).

In a particular implementation, the concentration of the p-type dopantin the second portion is uniform along a longitudinal dimension of theV-pits. In some embodiments, the concentration of the p-type dopant inthe V-pits, as measured along a longitudinal axis of the light emittingdevice, varies by at most about 50%, or 40%, or 30%, or 20%, or 10%, or5%, or 1%, or 0.1%, or 0.01%, or 0.001%, or 0.0001%. In other cases, theconcentration of the p-type dopant in the second portion is uniformalong a lateral dimension of the V-pits. In some embodiments, theconcentration of the p-type dopant in the V-pits, as measured along alateral axis of the light emitting device, varies by at most about 50%,or 40%, or 30%, or 20%, or 10%, or 5%, or 1%, or 0.1%, or 0.01%, or0.001%, or 0.0001%.

The light emitting device further comprises a substrate adjacent to then-type or p-type GaN layer. In an example, the substrate includessilicon, such as n-type silicon for example, or sapphire. In some cases,the substrate is for use in the completed light emitting device. Inother cases, the substrate is a carrier substrate and the completedlight emitting device, in such cases, will include another substrate. Insome embodiments, the substrate has a thickness ranging between about200 micrometers (um) and 2 millimeters (mm).

In some embodiments, the light emitting device includes a pit generationlayer. In some cases, the pit generation layer is adjacent to the n-typeGaN layer, such as below the n-type GaN layer and the active layer. Inother cases, the pit generation layer is between the n-type GaN layerand the active layer. The pit generation layer aids in the growth of theone or more V-pits during the formation of the active layer and, in somecases, other layers formed over the active layer.

In some embodiments, the pit generation layer has a defect densitybetween about 1×10⁸ cm ⁻² and 5×10⁹ cm ⁻², while in other embodimentspit generation layer has a defect density between about 1×10⁹ cm⁻² and2×10⁹ cm ⁻². In some embodiments, the pit generation layer has athickness between about 10 nm and 1000 nm, while in other embodiments,the pit generation layer has a thickness between about 50 nm and 500 nm.

The light emitting device includes an electrode in electricalcommunication with the n-GaN layer by direct contact with the n-GaNlayer or through one or more intervening layers. The light emittingdevice further includes an electrode in electrical communication with(or electrically coupled to) the p-GaN layer by direct contact with thep-GaN layer or through one or more intervening layers. In some cases,one or both of the electrodes have shapes and configurations (e.g.,location on the light emitting device) selected to minimize theobstruction of light emanating from the light emitting device.

The active layer may be a quantum well active layer, such as a multiplequantum well (MQW) active layer. In an embodiment, the active layercomprises a well layer formed of indium gallium nitride and/or indiumaluminum gallium nitride. The material comprising the active layer maybe compositionally graded (also “graded” herein) in two or more elementscomprising the active layer. In an example, the active layer is formedof graded indium gallium nitride, In_(x)Ga_(1-x)N, wherein ‘x’ is anumber between 0 and 1, and a barrier (or cladding) layer formed of GaN.The composition of such a layer may vary from a first side to a secondside of the layer. In some embodiments, the well or barrier material isselected from gallium nitride, various compositions (or stoichiometries)of InAlGaN and various compositions of AlGaN. In some embodiments, theactive layer has a thickness between about 10 nm and 1000 nm, while inother embodiments, the active layer has a thickness between about 50 nmand 200 nm.

In some embodiments, the active layer has a defect density between about1×10⁸ cm⁻² and 5×10⁹ cm⁻² while in other embodiments , the active layerhas a defect density between about 1×10⁹ cm⁻² and 2×10⁹ cm⁻². In otherembodiments, the active layer has a defect density greater than about1×10⁶ cm⁻², or greater than about 1×10⁷ cm⁻², or greater than about1×10⁸ cm ⁻², or greater than about 1×10⁹ cm⁻².

In some embodiments, the thickness of the light emitting device betweenthe n-GaN layer and the p-GaN layer is less than about 4 microns, orless than about 3 microns, or less than about 2 microns, or less thanabout 1 micron, or less than about 500 nm. The region between the n-GaNlayer and the p-GaN layer includes the active layer.

The light emitting device in some cases includes an electron blockinglayer between the active layer and the p-GaN layer. The electronblocking layer is configured to minimize the recombination of electronsand holes in the p-GaN layer, which may not desirable if opticalemission in the active layer is desired. In an example, the electronblocking layer is formed of aluminum gallium nitride or aluminum indiumgallium nitride. The electron blocking layer may be compositionallygraded (also “graded” herein) in two or more elements of the electronblocking layer. For instance, the electron blocking layer may be formedof graded aluminum gallium nitride, Al_(x)Ga_(1-x)N, wherein ‘x’ is anumber between 0 and 1, or Al_(x)In_(y)Ga_(1-x-y)N, wherein ‘x’ and ‘y’are numbers between 0 and 1. The composition of such a layer may varyfrom a first side to a second side of the layer. In some embodiments,the electron blocking layer has a thickness between about 1 nm and 1000nm, or between about 10 nm and 100 nm.

In some embodiments, the light emitting device further includes a p-typedopant injection layer between the active layer and the p-GaN layer. Thep-type dopant injection layer is configured to provide a p-type dopantto the second portion of the p-GaN layer during the formation of thep-GaN layer. The p-type dopant injection layer advantageously aids inproviding a desirable or predetermined concentration of a p-type dopantin the V-pits, which aids in minimizing, if not eliminating, issues withinadequately doped regions of the p-GaN layer. The p-type dopantinjection layer includes a p-type dopant and, in some cases, a wettingmaterial. In some embodiments, the p-type dopant is magnesium (Mg). Insome embodiments, the wetting material is indium (In). The wettingmaterial is configured to enable the p-type dopant to uniformly coverthe p-type dopant injection layer. In some cases, the wetting materialmay remain at the interface between the p-GaN layer and the electronblocking layer or active layer (if the electron blocking layer isprecluded).

In some embodiments, the p-type dopant injection layer has a thicknessthat is less than about 100 nm, or less than about 50 nm, or less thanabout 10 nm, or less than about 1 nm, or less. In some cases, thethickness of the p-type dopant injection layer is described in terms ofmonoatomic monolayers (ML). In some embodiments, the thickness of thep-type dopant injection layer is between about 0.1 ML and 10 ML. Inother embodiments, the p-type dopant injection layer has a thicknessless than or equal to about 10 ML, or less than or equal to about 5 ML,or less than or equal to about 4 ML, or less than or equal to about 3ML, or less than or equal to about 2 ML, or less than or equal to about1 ML, or less than or equal to about 0.5 ML, or less.

In some embodiments, a light emitting diode (LED) includes an n-typegallium nitride (GaN) layer, an active layer adjacent to said n-type GaNlayer, and a p-type GaN layer adjacent to the active layer. The activelayer includes one or more V-pits. The p-type GaN layer includes a firstportion and a second portion. The second portion is laterally bounded bythe one or more V-pits. The first portion is disposed over the activelayer and has a p-type dopant concentration of at least about 1×10¹⁸cm⁻³, or at least about 1×10¹⁹ cm⁻³, or at least about 1×10²⁰ cm⁻³, orat least about 1×10²¹ cm⁻³, or at least about 1×10²² cm⁻³. In somecases, the concentration of the p-type dopant is between about 1×10¹⁸cm⁻³ and 1×10²² cm⁻³, or between about 1×10¹⁹ cm⁻³ and 1×10²¹ cm⁻³, orbetween about 1×10²⁰ cm⁻³ and 5×10²⁰ cm⁻³.

In some embodiments, a light emitting diode (LED) includes a first layerof one of n-type gallium nitride (GaN) and p-type GaN, and an activelayer adjacent to the first layer, the active layer having one or moreV-pits. The LED further includes a second layer of the other of then-type GaN and p-type GaN, the second layer having a first portion and asecond portion laterally bounded by the one or more V-pits. The firstportion is disposed over the active layer. The second portion has auniform concentration of an n-type or p-type dopant.

FIG. 4 schematically illustrates a light emitting device (“device”) 400,in accordance with an embodiment of the invention. In an example, thelight emitting device 400 is a light emitting diode. The light emittingdevice 400 includes, from bottom to top, an n-doped (or “n-type”) GaNlayer (“n-GaN layer”) 405, a pit generation layer 410 adjacent to then-GaN layer 405, an active layer 415 adjacent to the pit generationlayer 410, an electron blocking layer 420 adjacent to the active layer415, a p-type dopant injection layer 425 adjacent to the electronblocking layer 420, and a p-GaN layer 430 adjacent to the p-type dopantinjection layer 425. The device 400 includes a plurality of V-pits 435(two shown), which form from defects (e.g., dislocations) in thematerial layers upon the layer-by-layer formation of the pit generationlayer 410, the active layer 415 and the electron blocking layer 420. Thep-GaN layer 430 includes a first portion 430 a and a second portion 430b, the second portion 430 b is disposed in the V-pits 435. The p-typedopant injection layer includes a p-type dopant and, in some cases, awetting material. The p-type dopant injection layer aids in forming thesecond portion 430 b with a desirable (or predetermined) uniformity,distribution and/or concentration of the p-type dopant in the secondportion 430 b.

In some embodiments, the active layer 415 is a multiple quantum wellactive layer. In an embodiment, the active layer is formed ofalternating layers of a well layer and a barrier layer, such asalternating layers of indium gallium nitride and gallium nitride, oralternating layers of indium aluminum gallium nitride and galliumnitride. Gallium nitride in both cases may serve as the barrier layermaterial. Indium gallium nitride or indium aluminum gallium nitride mayserve as a well layer material.

In an example, the active layer 415 is formed of alternating aluminumgallium nitride layers and gallium nitride layers, the electron blockinglayer 420 is formed of aluminum gallium nitride, and the p-type dopantinjection layer 425 is formed of magnesium and indium. Indium in such acase serves as the wetting material. Alternatively, the electronblocking layer 420 is formed of a quaternary material, such as aluminumindium gallium nitride. In some cases, the electron blocking layer 420is compositionally graded. In other cases, the electron blocking layer420 has a uniform composition.

The device 400 is formed on a substrate (not shown). The substrate isdisposed adjacent to the n-GaN layer 405 or adjacent to the p-GaN layer430. In an embodiment, the substrate is formed of silicon or sapphire.In some cases, the substrate is disposed adjacent to the n-GaN layer405, and a buffer layer having an AlN layer and an AlGaN layer is formedbetween the substrate and the n-GaN layer 405. The AlN layer is disposedadjacent to the substrate, and the AlGaN layer is disposed adjacent tothe AlN layer and the n-GaN layer 405.

In an implementation, the substrate is formed of silicon disposedadjacent to the n-GaN layer 405. The substrate may be used to transferthe layers 405-430 to another substrate, such as silicon. In such acase, with the layers 405-430 formed on a first substrate disposedadjacent to the n-GaN layer, after transfer, the layers 405-430 aredisposed on a second substrate adjacent to the p-GaN layer.

FIG. 5 schematically illustrates a device 500 having a plurality oflayers 510-535 formed on a substrate 505, in accordance with anembodiment of the invention. The device 500 is a light emitting device,such as a light emitting diode. The device 500 includes, from bottom totop (with “bottom” designating a location adjacent to the substrate505), an n-GaN layer 510, a pit generation layer 515, an active layer520, an electron blocking layer 525, a delta doped layer 530, and ap-GaN layer 535. The p-GaN layer 535 includes a first portion and asecond portion (not shown). The second portion is formed in one or moreV-pits in the pit generation layer 515, the active layer 520 and theelectron blocking layer 525 (see, e.g., FIG. 4). The delta-doped layer530 includes a p-type dopant, such as magnesium, and a wetting material,such as indium. In some situations, the wetting material decreases thebarrier to migration of a p-type dopant on a surface of the delta-dopedlayer, enabling the p-type material to uniformly cover the delta-dopedlayer. The wetting material may reduce the surface energy of the p-typedopant (e.g., Mg) on the V-defect. As described below, the p-type dopantis provided in the delta doped layer 530 by pulsing a source gas of thep-type dopant into a reaction chamber having the substrate 505.

In an example, the delta doped layer 530 includes a wetting material,such as indium, which reduces the surface energy of a p-type dopant(e.g., Mg) on the V-defect facets, thereby aiding in the incorporationof the p-type dopant into the wetting layer. The p-type dopant in thedelta doped layer 530 provides a source of the p-type dopant forsubsequent incorporation into a portion of the GaN layer in one or moreV-pits of the active layer 520 and the electron blocking layer 525. Thisfacilitates the formation of the portion of the p-GaN layer 535 in theone or more V-pits.

In some embodiments, the device 500 includes a first electrode inelectrical communication with the n-GaN layer 510 and a second electrodein electrical communication with the p-GaN layer 535. The electrodesenable the application of an electrical potential (voltage) across theactive layer 520. In some situations, the first and second electrodesare in electrical contact with the n-GaN layer 510 and the p-GaN layer535, respectively. In other cases, one or both of the first and secondelectrodes are in electrical contact with the n-GaN layer 510 and thep-GaN layer 535 through one or more intervening layers. In an example,the second electrode is in electrical communication with the p-GaN layerthrough a transparent conductive layer (not shown), such as, forexample, an indium tin oxide (ITO) layer.

The recombination of electrons and holes in the active layer 520, suchas upon the application of an electrical potential across the activelayer 520, generates light which is transmitted out of the device in adirection generally away from the substrate 505. As an alternative, thelayers 505-535 are transferred to another substrate 540 and thesubstrate 505 is subsequently removed. The recombination of electronsand holes in the active layer 520 generates light, which is subsequentlytransmitted out of the device 500 through the n-GaN layer and along adirection generally away from the substrate 540. In some cases, thedevice 500 includes additional layers between the p-GaN layer 535 andthe substrate 540.

In some embodiments, the substrate 505 is formed of one or more ofsilicon, silica, sapphire, zinc oxide, carbon (e.g., graphene), SiC, AN,GaN, spinel, coated silicon, silicon on oxide, silicon carbide on oxide,glass, gallium nitride, indium nitride, titanium dioxide, aluminumnitride, a metallic material (e.g., copper), and combinations (oralloys) thereof. In some situations, the substrate 505 is formed ofsilicon. In an example, the substrate 505 can be formed of n-typesilicon. In such a case, an electrode may be formed in contact with thesubstrate 505 that is in electrical communication with the n-GaN layer510.

The device 500, in some cases, includes one or more additional layersbetween the substrate 505 and the n-GaN layer 510. The one or moreadditional layers may include buffer layers, stress relaxation layers,or stress generation layers. In an embodiment, the device 500 includesan aluminum gallium nitride layer adjacent to the substrate, and one ormore u-type GaN (i.e., undoped or unintentionally doped GaN) layersadjacent to the aluminum gallium nitride layer. The one or more u-GaNlayers are disposed adjacent to the n-GaN layer 510.

In some situations, the electron blocking layer 525 is formed ofaluminum gallium nitride (AlGaN). In some cases, the AlGaN layer can becompositionally graded in aluminum and gallium.

In some embodiments, the delta doped layer 530 is at an interfacebetween the electron blocking layer 525 and the p-GaN layer 535. In somecases, at the interface between the electron blocking layer 525 and thep-GaN layer 535, the device 500 has a secondary ion mass spectrometry(SIMS) profile exhibiting coincident Mg and In peaks.

In some cases, as measured by SIMS, the peak indium intensity observedwithin the delta-doped layer 530 is on the order of 1/100th or less thanthe peak indium intensity (or concentration) observed in the individualquantum wells within the active layer 520. The position of the peakindium concentration coincides with that of the peak magnesiumconcentration at the interface between the AlGaN layer and the p-GaNlayer 535.

In some embodiments, a light emitting device with V-pits (or V-defects)has a uniform distribution of a p-type dopant in a p-GaN layer of thelight emitting device. This advantageously enables the use of devicestructures (e.g., active layer) with moderate to high defect densities,while minimizing, if not eliminating, the issues with such devicestructures provided herein, such as non-uniform dopant concentrations.

Methods for Forming Light Emitting Devices

In another aspect of the invention, methods for forming a light emittingdevice are provided. Such methods provide for the formation of devicesdescribed herein, such as light emitting diodes, including Group III-VLED's (e.g., GaN-based LED's).

In some embodiments, a method for forming a light emitting device, suchas a light emitting diode (LED), includes forming, over a substrate in areaction chamber, a p-type Group III-V semiconductor layer over (oradjacent to) an active layer, the p-type Group III-V semiconductor layerextending into one or more V-pits of the active layer, including anyintervening layers between the p-type Group III-V semiconductor layerand the active layers (e.g., an electron blocking layer). The p-typeGroup III-V semiconductor layer is formed by delta doping a wettinglayer with a p-type dopant, and introducing a Group III source gas and aGroup V source gas into the reaction chamber. A source gas of a p-typedopant is introduced to control the concentration of the p-type dopantin the p-type Group III-V layer. The active layer is formed over (oradjacent to) an n-type Group III-V semiconductor layer. The Group III-Vsemiconductor layer is formed by introducing a Group III source gas, aGroup V source gas and a source gas of an n-type dopant into thereaction chamber.

The p-type Group III-V semiconductor layer includes a Group III-Vsemiconductor and a p-type dopant. The n-type Group III-V semiconductorlayer includes a Group III-V semiconductor and an n-type dopant. A GroupIII-V semiconductor includes a Group III species and a Group V species.In an embodiment, a Group III species is gallium and/or indium. Inanother embodiment, a Group V species is nitrogen.

In some embodiments, a method for forming a light emitting device, suchas an LED, includes forming, over a substrate in a reaction chamber, ap-type Group III-V semiconductor layer adjacent to an active layer, thep-type Group III-V semiconductor layer extending into one or more V-pitsof the active layer. The p-type Group III-V semiconductor layer isformed by delta doping a wetting layer with a p-type dopant andintroducing a source gas of a Group III species and a source gas of aGroup V species into the reaction chamber. The wetting layer is formedadjacent to the active layer. In some situations, prior to forming thewetting layer, an electron blocking layer is formed adjacent to theactive layer. In an embodiment, the active layer is formed adjacent toan n-type Group III-V semiconductor layer. In another embodiment, then-type Group III-V semiconductor layer is formed adjacent to thesubstrate.

In a particular implementation, a method for forming a light emittingdiode (LED) comprises forming, over a substrate in a reaction chamber, ap-type gallium nitride (p-GaN) layer over (or adjacent to) an activelayer, the p-GaN layer extending into one or more V-pits of the activelayer, including any intervening layers between the p-GaN layer and theactive layers (e.g., an electron blocking layer). The p-GaN layer isformed by delta doping a wetting layer with a p-type dopant, andintroducing a gallium source gas and a nitrogen source gas into thereaction chamber. A source gas of a p-type dopant is introduced tocontrol the concentration of the p-type dopant in the p-GaN layer.

In an embodiment, the wetting layer is formed adjacent to the activelayer. In some cases, the light emitting device includes an electronblocking layer formed between the wetting layer and the active layer. Insome situations, prior to forming the wetting layer, an electronblocking layer is formed adjacent to the active layer. The active layeris formed over (or adjacent to) an n-type GaN (“n-GaN”) layer. The n-GaNlayer is formed over (or adjacent to) the substrate.

In other embodiments, a method for forming a light emitting diode (LED)includes forming an n-GaN layer adjacent to a substrate in a reactionchamber, forming an active layer over the substrate, forming an electronblocking layer over the active layer, and forming a delta-doped layerover the electron blocking layer. The delta-doped layer is formed bydelta doping a wetting layer with a p-type dopant.

In some situations, delta doping the wetting layer includes pulsing aprecursor of the p-type dopant into a reaction chamber having thesubstrate. The precursor of the p-type dopant is pulsed for a durationbetween about 0.01 seconds and 20 minutes, or between about 0.1 secondsand 15 minutes, or between about 1 second and 10 minutes.

FIG. 6 schematically illustrates a method 600 having a process flowdiagram for forming a light emitting device, in accordance with anembodiment of the invention. In a first operation 605, a substrate isprovided in a reaction chamber configured for growth of one or moredevice structures (or layers) of the light emitting device. In anexample, the reaction chamber is a chamber under vacuum or an inert gasenvironment.

For instance, the reaction chamber may be a vacuum chamber, such as anultrahigh vacuum (UHV) chamber. In cases in which a low-pressureenvironment is desired, the reaction chamber may be pumped with the aidof a pumping system having one or more vacuum pumps, such as one or moreof a turbomolecular (“turbo”) pump, a cryopump, an ion pump and adiffusion pump and a mechanical pump. The reaction chamber may include acontrol system for regulating precursor flow rates, substratetemperature, chamber pressure, and the evacuation of the chamber.

Next, in a second operation 610, an n-GaN layer is formed over thesubstrate. In an embodiment, the n-GaN layer is formed by directing intothe reaction chamber a gallium precursor, a nitrogen precursor, and aprecursor of an n-type dopant. The gallium precursor includes one ormore of trimethylgallium (TMG), triethylgallium, diethylgallium chlorideand coordinated gallium hydride compounds (e.g., dimethylgalliumhydride). The nitrogen precursor includes one or more of ammonia (NH₃),nitrogen (N₂), and plasma-excited species of ammonia and/or N₂. In somecases, the precursor of the n-type dopant is silane.

In an embodiment, the gallium precursor, the nitrogen precursor and theprecursor of the n-type dopant are directed into the reaction chambersimultaneously. In another embodiment, the gallium precursor, thenitrogen precursor and the precursor of the n-type dopant are directedinto the reaction chamber (e.g., pulsed) in an alternating andsequential basis.

Next, in an optional third operation 615, a pit generation layer isformed over the n-GaN layer. The pit generation layer is formed bydirecting into the reaction chamber a gallium precursor and a nitrogenprecursor, and in some cases an indium precursor. The pit generationlayer in some situations is formed of GaN, InGaN, and variouscombinations thereof, including an InGaN/GaN superlattice. In somecases, the pit generation layer is optional if one or more sub-layers ofa multiple quantum well active layer are used to create pits.

Next, in a fourth operation 620, an active layer is formed over then-GaN layer or the pit generation layer (if formed in operation 615). Inan example, the active layer is a multiple quantum well active layercomprising alternating InGaN well layers and GaN barrier layers. Theactive layer is formed by during a gallium source gas and a nitrogensource gas into the reaction chamber to form a barrier layer, andintroducing an indium source gas to form a well layer. The indium sourcegas includes one or more of trimethylindium, triethylindium,diethylindium chloride and coordinated indium hydride compounds (e.g.,dimethylindium hydride). The source gases for forming the individualbarrier and well layers are directed into the reaction chambersimultaneously or, in other cases, alternately and sequentially.

Next, in a fifth operation 625, an electron blocking layer is formedover the active layer. In cases in which the electron blocking layerincludes aluminum gallium nitride, the electron blocking layer is formedby directing into the reaction chamber a gallium source gas, a nitrogensource gas and an aluminum source gas. In some situations, the aluminumsource gas includes one or more of tri-isobutyl aluminum (TIBAL),trimethyl aluminum (TMA), triethyl aluminum (TEA), and dimethylaluminumhydride (DMAH). In some situations, the electron blocking layer includesaluminum indium gallium nitride, in which case an indium source gas,such as trimethylindium (TMI), may be used in conjunction with othersource gases. In other embodiments, the electron blocking layer in somecases is precluded.

Next, in a sixth operation 630, a wetting layer is formed over theelectron blocking layer (or the active layer if the electron blockinglayer is precluded). The wetting layer is formed by directing into thereaction chamber a source gas of a wetting material, such astrimethylindium (TMI) if the wetting material is indium.

Next, in a seventh operation 635, the wetting layer is contacted with asource gas of a p-type dopant. In an implementation, the wetting layeris delta doped by pulsing into the reaction chamber the source gas ofthe p-type dopant. Delta doping the wetting layer forms a delta dopedlayer. In some cases, the delta doped layer is a p-type dopant injectionlayer. In an example, the p-type dopant is magnesium, and the wettinglayer is delta doped with magnesium by directing into the reactionchamber biscyclopentadienyl magnesium (Cp2Mg).

In an example, the wetting layer is formed at operation 630 at a firsttemperature and in operation 635 the wetting layer is delta doped at thesame or similar temperature to form the delta doped layer. However, inother cases, the wetting layer is formed at a first temperature, and thewetting layer is delta doped with a p-type dopant at a secondtemperature that is different from the first temperature. In anembodiment, the wetting layer and/or the delta doped layer are formed ata temperature between about 700° C. and 1100° C. In other embodiments,the wetting layer and/or the delta doped layer are formed at atemperature between about 800° C. and 1050° C., while in otherembodiments, the wetting layer and/or the delta doped layer are formedat a temperature between about 850° C. and 1000° C.

In an example, the wetting layer is delta doped by pulsing into thereaction chamber a source gas of a p-type dopant. In an embodiment, thesource gas of the p-type dopant is pulsed for a duration between 0.01seconds and 20 minutes. In other embodiments, the source gas of thep-type dopant is pulsed for a duration between about 0.1 seconds and 15minutes, while in other embodiments, the source gas of the p-type dopantis pulsed for a duration between about 1 second and 10 minutes.

In the illustrated example, operation 635 follows operation 630. In somecases, however, operations 630 and 635 are performed simultaneously.That is, the source gas of the wetting material and the source gas ofthe p-type dopant are directed into the reaction chamber simultaneously.In an example, trimethylindium (TMI), biscyclopentadienyl magnesium(Cp2Mg) and ammonia are directed into the reaction chamber with the aidof an N₂ carrier gas and brought in contact with the electron blockinglayer (e.g., AlGaN) formed in operation 625. The Cp2Mg may be flowedbefore, concurrently, or after providing TMI into the reaction chamber.In an example, operation 635 precedes operation 630—that is, theelectron blocking layer is contacted with the source of the p-typedopant (e.g., Cp2Mg) to form a layer of a p-type dopant over theelectron blocking layer, which is subsequently contacted with the sourcegas of the wetting material (e.g., TMI).

Next, in an eight operation 640, a p-type gallium nitride (p-GaN) layeris formed over (or adjacent to) the delta doped layer. In someembodiments, no actual growth of the p-GaN layer occurs during theformation of the delta doped layer.

The p-GaN layer is formed by directing into the reaction chamber agallium source gas (or precursor) and a nitrogen source gas. In anembodiment, a source gas of a p-type dopant is not directed into thereaction chamber with the gallium source gas and the nitrogen sourcegas. In such a case, upon bringing the gallium source gas and thenitrogen source gas in contact with the delta doped layer, a GaN layerbegins to form on the delta-doped layer. Growth of the GaN layer isaccompanied by the incorporation of the p-type dopant from the deltadoped layer into the GaN layer, thereby forming the p-GaN layer, whichis accompanied by a depletion of the delta doped layer in the p-typedopant. At a predetermined period of time, a source gas of a p-typedopant is introduced into the reaction chamber to continue the formationof the p-GaN layer. In some cases, the source gas of the p-type dopantis accompanied by a continuing flow of gallium source gas and nitrogensource gas. The delta doped layer enables doping of the GaN layer (toform p-GaN) in one or more V-pits of the active layer and the electronblocking layer. Subsequent introduction of the source gas of the p-typedopant provides the p-type dopant for continual growth of the p-GaNlayer in a portion of the p-GaN layer over the active layer (and not inthe V-pits).

In an example, a p-GaN layer includes a first portion and a secondportion (see, e.g., FIG. 4). The first portion is disposed over theelectron blocking layer outside of the one or more V-pits, and thesecond portion is formed in the one or more V-pits. During growth of thesecond portion, the p-type dopant for the p-GaN layer is provided by thedelta doped layer. Following formation of the second portion, a sourcegas of the p-type dopant (or a source gas of another p-type dopant) isintroduced to provide a predetermined concentration of the p-type dopantin the first portion.

In some situations, source gases are directed into the reaction chamberwith the aid of a carrier gas and/or pumping. The carrier gas may be aninert gas, such as H₂, Ar and/or N₂. In an example, a gallium source gas(e.g., TMG) and a nitrogen source gas (e.g., NH₃) are directed into thereaction chamber with the aid of N₂. In another example, a galliumsource gas, a nitrogen source gas and a source gas of a p-type dopantare directed into the reaction chamber with the aid of a pumping system(e.g., turbo pump).

The reaction chamber between some or all of the individual operationsmay be evacuated. In some cases, the reaction chamber is purged with theaid of a purge gas or a vacuum (pumping) system. In an example, thereaction chamber between operations 620 and 625 is evacuated with theaid of a purge gas. The purge gas may be the same or similar as thecarrier gas. In an example, the purge gas is N₂, and the reactionchamber is purged by continuing the flow of N₂ into the reaction chamberwhile terminating the flow of one or more source gases. In anotherexample, the reaction chamber between operations 610 and 615 isevacuated with the aid of a pumping system (i.e., applying a vacuum tothe reaction chamber). In other cases, a reaction chamber is purged withthe aid of a purge gas and a vacuum system.

While method 600 has been described as occurring in a reaction chamber,in some situations, one or more of the operations of the method 600 canoccur in separate reaction chambers. In an example, operations 605 and610 are conducted in a first reaction chamber, operations 615-625 areconducted in a second reaction chamber, and operations 630-640 areconducted in a third reaction chamber. The reactions spaces may befluidically isolated from one another, such as in separate locations.

FIG. 7 shows a pressure vs. time pulsing diagram for forming a deltadoped layer and a p-GaN layer over the delta doped layer. Pressure(y-axis) is shown as a function of time (x-axis). The pressure maycorrespond to the partial pressure of each source gas in the reactionchamber. With a substrate in a reaction chamber, at a first time (t₁),TMI and NH₃ are directed into the reaction chamber with the aid of an N₂carrier gas. This forms a wetting layer over the substrate. Next, thewetting layer is delta doped with Mg with the aid of Cp2Mg, which isdirected into the reaction chamber at a second time (t₂). The flow ratesof NH₃ and N₂ are maintained during the pulse of Cp2Mg into the reactionchamber. The time period for Cp2Mg exposure is less than that of TMI;however, in some situations, the time period (i.e., pulse duration) forCp2Mg exposure is greater than or equal to the time period for TMIexposure. The Cp2Mg pulse overlaps the TMI pulse. In other cases, theCp2Mg pulse does not overlap the TMI pulse. In an example, the Cp2Mgpulse precedes the TMI pulse. In another example, the Cp2Mg pulsefollows the TMI pulse.

Next, at a third time (t₃), TMG is directed into the reaction chamber.Prior to the introduction of TMG, the flow rate of Cp2Mg is terminated,but the flow rates of NH₃ and N₂ are maintained. Next, at a fourth time(t₄), Cp2Mg is directed into the reaction chamber to provide a p-typedopant for forming the p-GaN layer. The delta doped layer provides ap-type dopant (Mg) for incorporation into V-pits upon GaN deposition,which forms p-GaN in the V-pits. The second dose of Cp2Mg provides ap-type dopant for the subsequent growth of the p-GaN layer over thesubstrate and outside of the V-pits.

One or more layers of light emitting devices provided herein may beformed by a vapor (or gas phase) deposition technique. In someembodiments, one or more layers of the light emitting devices providedherein are formed by chemical vapor deposition (CVD), atomic layerdeposition (ALD), plasma enhanced CVD (PECVD), plasma enhanced ALD(PEALD), metal organic CVD (MOCVD), hot wire CVD (HWCVD), initiated CVD(iCVD), modified CVD (MCVD), vapor axial deposition (VAD), outside vapordeposition (OVD) and/or physical vapor deposition (e.g., sputterdeposition, evaporative deposition).

While methods and structures provided herein have been described in thecontext of light emitting devices having certain Group III-Vsemiconductor materials, such as gallium nitride, such methods andstructures may be applied to other types of semiconductor materials.Methods and structures provided herein may be used with light emittingdevices having active layers formed of gallium nitride (GaN), indiumgallium nitride (InGaN), zinc selenide (ZnSe), aluminum nitride (AlN),aluminum gallium nitride (AlGaN), aluminum gallium indium nitride(AlGaInN) and zinc oxide (ZnO).

In some embodiments, layers and device structures provided herein, suchas, for example, active layers (including well layers and barrierlayers), n-type Group III-V semiconductor layers, p-type Group III-Vsemiconductor layers, are formed with the aid of a controller that isconfigured to regulate one or more processing parameters, such as thesubstrate temperature, precursor flow rates, growth rate, hydrogen flowrate and reaction chamber pressure. The controller includes a processorconfigured to aid in executing machine-executable code that isconfigured to implement the methods provided herein.

EXAMPLE

A substrate having an AlGaN electron blocking layer over an active layeris provided in a reaction chamber. The active layer and electronblocking layer include a plurality of V-pits. A p-GaN layer is formed onthe AlGaN electron blocking layer by initially forming a p-type deltadoped layer. At a substrate temperature between about 850° C. and 1000°C., trimethylindium (TMI) and ammonia (NH₃) are provided into thereaction chamber with the aid of an N₂ carrier gas and brought incontact with the electron blocking layer to form a wetting layer. Next,the wetting layer is delta doped with magnesium by directing Cp2Mg intothe reaction chamber and exposing the wetting layer to Cp2Mg. In somecases, Cp2Mg is provided into the reaction chamber before, concurrentlywith, or after flowing TMI into the reaction chamber. Next, a layer ofGaN is formed on the delta doped layer by introducing TMG into thereaction chamber. The p-type dopant in the delta doped layer providesp-type dopant for incorporation into the GaN layer in the V-pits. Priorto or subsequent to the p-GaN layer filling the V-pits, a source gas ofa p-type dopant is introduced into the reaction chamber along with TMGand NH₃. The timing of the source gas of the p-type dopant is selectedto provide a p-type dopant concentration, distribution and/ordistribution as desired.

Unless the context clearly requires otherwise, throughout thedescription and the claims, words using the singular or plural numberalso include the plural or singular number respectively. Additionally,the words ‘herein,’ hereunder,“above,”below,' and words of similarimport refer to this application as a whole and not to any particularportions of this application. When the word ‘or’ is used in reference toa list of two or more items, that word covers all of the followinginterpretations of the word: any of the items in the list, all of theitems in the list and any combination of the items in the list.

It should be understood from the foregoing that, while particularimplementations have been illustrated and described, variousmodifications may be made thereto and are contemplated herein. It isalso not intended that the invention be limited by the specific examplesprovided within the specification. While the invention has beendescribed with reference to the aforementioned specification, thedescriptions and illustrations of embodiments of the invention hereinare not meant to be construed in a limiting sense. Furthermore, it shallbe understood that all aspects of the invention are not limited to thespecific depictions, configurations or relative proportions set forthherein which depend upon a variety of conditions and variables. Variousmodifications in form and detail of the embodiments of the inventionwill be apparent to a person skilled in the art. It is thereforecontemplated that the invention shall also cover any such modifications,variations and equivalents.

What is claimed is:
 1. A light emitting device comprising: an n-typegallium nitride layer; an active layer adjacent to the n-type galliumnitride layer, the active layer comprising indium (In); an electronblocking layer adjacent to the active layer; and a p-type galliumnitride layer adjacent to the electron blocking layer, wherein the lightemitting device comprises indium (In) at an interface between theelectron blocking layer and the p-type gallium nitride layer, an Inintensity having a first peak in the interface and a second peak in theactive layer, the first peak of the In intensity in the interface beinglower than the second peak of In intensity in the active layer, andwherein the p-type gallium nitride layer extends into one or more V-pitsof the active layer.
 2. The light emitting device of claim 1, whereinthe active layer has a dislocation density between about 1×10⁸ cm⁻² and5×10⁹ cm⁻².
 3. The light emitting device of claim 1, wherein theelectron blocking layer comprises aluminum gallium nitride (AlGaN). 4.The light emitting device of claim 1, wherein the electron blockinglayer comprises aluminum indium gallium nitride (AlInGaN).
 5. The lightemitting device of claim 1, wherein the first peak of the In intensityin the interface is 1/100th or lower than the second peak of the Inintensity in the active layer.
 6. The light emitting device of claim 1,wherein the interface is a layer comprising In and N.
 7. The lightemitting device of claim 1, further comprising a substrate adjacent tothe n-GaN layer.
 8. The light emitting device of claim 7, wherein thesubstrate is a silicon substrate.
 9. The light emitting device of claim1, further comprising a pit generation layer between the n-type galliumnitride layer and the active layer, the one or more V-pits generated inthe pit generation layer.
 10. The light emitting device of claim 1,wherein the p-type gallium nitride layer has a first portion and asecond portion, the first portion disposed over the active layer, thesecond portion laterally bounded by the one or more V-pits.
 11. Thelight emitting device of claim 10, wherein a concentration of a p-typedopant in the first portion is at least about 1×10²⁰ cm⁻³.
 12. The lightemitting device of claim 10, wherein a concentration of a p-type dopantin the second portion is at least about 1×10²⁰ cm⁻³.
 13. The lightemitting device of claim 10, wherein a first concentration of a p-typedopant in the first portion and a second concentration of a p-typedopant in the second portion are at least about 1×10^(°)cm⁻³.